BREAKING THE CONNECTION - DISPLACEMENT OF THE DESMOSOMAL PLAQUE PROTEIN DESMOPLAKIN FROM CELL-CELL INTERFACES DISRUPTS ANCHORAGE OF INTERMEDIATE FILAMENT BUNDLES AND ALTERS INTERCELLULAR JUNCTION ASSEMBLY

The desmosomal plaque protein desmoplakin (DP), located at the junctur e between the intermediate filament (IF) network and the cytoplasmic t ails of the transmembrane desmosomal cadherins, has been proposed to l ink IF to the desmosomal plaque. Consistent with this hypothesis, prev ious studies of individual DP domains indicated that the DP COOH termi nus associates with IF networks whereas NH2-terminal sequences govern the association of DP with the desmosomal plaque, Nevertheless, it had not yet been demonstrated that DP is required for attaching IF to the desmosome, To test this proposal directly, we generated A431 cell lin es stably expressing DP NH2-terminal polypeptides, which were expected to compete with endogenous DP during desmosome assembly. As these pol ypeptides lacked the COOH-terminal IF-binding domain, this competition should result in the loss of IF anchorage if DP is required for linki ng IF to the desmosomal plaque. In such cells, a 70-kD DP NH2-terminal polypeptide (DP-NTP) colocalized at cell-cell interfaces with desmoso mal proteins. As predicted, the distribution of endogenous DP was seve rely perturbed, At cell-cell borders where endogenous DP was undetecta ble by immunofluorescence, there was a striking absence of attached to nofibrils (IF bundles). Furthermore, DP-NTP assembled into ultrastruct urally identifiable junctional structures lacking associated IF bundle s. Surprisingly, immunofluorescence and immunogold electron microscopy indicated that adherens junction components were coassembled into the se structures along with desmosomal components and DP-NTP. These resul ts indicate that DP is required for anchoring IF networks to desmosome s and furthermore suggest that the DP-IF complex is important for gove rning the normal spatial segregation of adhesive junction components d uring their assembly into distinct structures.